Electronic and geometric structures of aluminum-boron negative cluster ions (Al nB −m)

Abstract

Aluminum-boron negative cluster ions (Al n B − m , n=5–30, m=1–3) were generated by two independent laser-vaporization sources. The mass distribution of Al n B − 2 exhibits one peak at n=12 and one step between n=22 and 23 as magic numbers, whereas that of Al n B − 2 exhibits only one step between n=21 and 22. The loss of the magic number of Al 11B − 2 can be explained by the geometric structures: Al 12B − 1 is stabilized by both an electronic shell closing of the 2p shell and a close-packing structure of icosahedron. In contrast, Al 11B − 2 can satisfy the electronic shell closing by cannot take the stable geometric structure because the diameters of Al and B atoms differ largely. The structure of Al 12B − 1 can be an icosahedron with a B atom located at the center.